A longtime Brockton administrator has been named principal of Brockton High School. Sharon R. Wolder, the district’s associate principal of curriculum and instruction, succeeds Susan Szachowitz, who retired in December. City and school leaders lauded Wolder for the experience and continuity she brings to the 4,200-student school, the largest high school in the state. “Sharon has been an integral part of Brockton High School’s proven model of academic success,” said interim Superintendent John Jerome. “She understands the complex issues that our students face.” Wolder, a native of Iowa who lives in Brockton, started work there as a history teacher in 1995 and also served as head of the social science department, housemaster of the Red House, and associate principal.